Transmission mechanism of the fluid shear type



B. N. PALM 2,954,857

.TRANSMISSION MECHANISM oF THE FLUID SHEARITYPE: i

2 Sheets-Sheet 1 Oct. 4, 1960 Filed Jan. 3, 1958 Oct. 4, 1960 Filed Jan. 5, 1958 2 Sheets-Sheet 2 im@ Mfr United States Patent 4-hlice 2,954,857 Patented ct. 4, 1960 'mANsMIssIoN oF THE l FLUID sHEAR TYPE Bernhard N. Palm, Newport Beach, Calif., assignr to v fEleetra Motors, Inc., Anaheim, Calif., a corporation of California Filed Jan. 3, 1958, Ser. No. 707,029 Claims. (Cl. 192-58) This invention relates to improvements in a typeof fluid shear transmissions wherein the transmitted torque f varies as a function of the slip between the driving and driven elements. The improvements of the invention include, among other things, the design and arrangement of the driving and driven elements to enablethem to be maintained during operation in fixed spatial relation to each other, with no variation in spacing due to imbalances of duid pressures; and, generally, the extreme simplilication of design, reduction in cost, and uniformity and reliability of operation.

In a previous huid shear transmission, the spaced opposing active driving areas are the opposed surfaces of disks centrally mounted on the driving and driven members, respectively. Varying unbalanced pressures on opposite sides of those disks cause disk flexure, lresulting in Variations of spacing and thus in uncontrolled variations of transmitted torque. As will be explained, the present invention completely overcomes that deficiency and greatly simplifies the whole transmission structure.

In a typical and illustrative form of the present invention the disk member is enclosed within the other member which is in the form of a rigid housing rotatable relative to the disk member. In such an illustrative form, the active driving faces are the opposite faces of a disk, each opposed by spaced faces of the rigid housing. VPressures on the disk, as well as on the housing, are, by this arrangement, balanced; eliminating distortion and variation of spacing. And the structure is also greatly simplified. Y Y

These and other objects and accomplishments of the invention, will be best understood from the following descriptions of presently preferred illustrative embodiments shown in the drawings, in which:

Fig. 1 is a longitudinal central section of one typical embodiment;

Fig. la is a schematic illustrating operation;

Figs. lb and 1c are diagrams showing typical performance curves;

Fig. 2 is a section taken as indicated by line 2 2 on Fig. 1; Y

Fig. 3 is a section similar to that of Fig. l, showing a modification; and

Fig. 4 is a similar section showing another cation.

Referring first lto Figs.V 1 and 2; a housing is composed of two substantially identical parts 10 and 12, secured together in rigid and uid tight relation by suitable means, not shown. In the housing as thusl composed there is an annular cavity 14, within which the circular disk 16 rotates with its opposite faces inspaced relation to certain wall surfaces of the cavity, as explained below. Disk 16 is rotationally xed on a hub 18 (see below) which hub is journaled in bearing sleeves 20, of any suitable type, mounted in the hub portions 22 of the two housing halves 10 and 12. Shaft 24 drives, or is driven by, hub 18. In such an arrangement` the shaft may carry the housing. In a typical design hub 18 is modifirigidly mounted on shaft 24, in effect integral with it. The drive to or from the housing is taken oif in any desired manner; for example, through a flange attached to hub 22 of housing half 12. Regardless of how hub 18 is supported and driven, and of how the drive is applied to or taken off the housing, the housing is freely rotatable, on the axis of hub 18 and'disk 16, relative to the disk.

The housing, and its cavity surfaces may be held in iixed axial position relative to the disk by suitable end thrust arrangements. As an example, suitable end thrust rings are shown at 30 located between housing shoulders 32 and hub shoulders 34. These rings also act to prevent leakage of fluid from the housing cavity around the hub. If the disk is rigidly mounted on the hub, these end thrust rings may perform the function Aof xedly spacing the opposed surfaces of the disk and housing. But, although the disk may be rigidly mounted on the hub, preferably it is splined to it, by splines or keys such as indicated in Fig. 1 at 19. The disk is then held in its proper spaced relation by the opposing balanced pressures on its opposite faces.

To insure accurate concentricity between the two housing halves, a iiuid tight peripheral joint is formed as shown at 34. Other than atthis joint formation, the halves are duplicates in all their functional formations.

Fig. 2 shows an inner facial view of housing half 10.V

ln all functional formations that view also applies to the half 12.

As thus shown in the drawings, each half contains an essentially duplicate part of the cavity 14. That cavity ineach half has an outer active part lying within and outwardly boundedV by the peripheral shoulder 40 and having a dat radial wall surface 42 closely spaced in parallelism to the opposite faces 44 of disk 16. Immediately surrounding the hub portions of the body is an annular fluid reservoir 46. The reservoir parts of the cavity are sunk into the opposed faces of the halves much deeper than are the active cavity parts, as clearly shown in Fig. l. The line at 48 indicates the circumferential delimitation between reservoirs 46 and the active outer annular spaces A between the radial faces 42 and disk faces V44. Along that whole line of delimitationthe outer boundary of the reservoirs and the inner boundary of active spaces A-those spaces are in communication with the reservoirs.

Leading outwardly from reservoirs 46 is a passage means consisting preferably of a plurality of passages (here shown as three). In Figs. l and 2 those passages are shown as slots 50 sunk into the housing halves beyond the cavity surfaces 42. These slots at their inner ends are in open communication with the reservoirs, and their outer ends are located on a circle at a radius indicated as R in Figs. la and 2, from the central axis C. Radius R is less than radius R1 of the shoulder 40 that defines the outer limit of active faces 42. Each active face 42 thus has an outer continuous annular area 42a. unbroken by the passages 50. The circumference of disk 16 is spaced slightly inwardly of the delimiting shoulder 40 of surfaces A42. Thus the opposite faces 44 of the disk are in spaced parallel opposition to the whole of active surfaces 42, including the outer annular areas 42a and the areas inwardof that annular area lying between passages 50 and inwardly delimited by the reservoirs at 48. A typical dimension of that spacing is 0.020 inch. The peripheral spacing at shoulder 40 may also preferably be the same; although it may be more. Circumferential grooves such as shown at 51 in Figs. l and 2 leading from the outer ends of passages 50 may be used, if desired, to facilitate the uid movements herein described.

Various fluids may be used in the described transmission. At present silicon fluids are preferred because of their approximately constant viscosity under changing temperature, and their chemical stability. The viscosity chosen may range from fifty to one thousand centistoke's, depending on the amount of powerftobe transmitted; Figs. 1 and 2 show an actual operating transmissionapproximately to scale; the dimensions VmaybeV scaled by taking shaft 24 to be three-quarters o'foneY inch in diameter. A transmission ,of that siz'e will transmit, with the driving shaft rotating at 175() r.p.m., a'range of power from approximately 1A H.P. to 3A HP., depending onthe chosen fluid viscosity. l

The housing is charged'with the amount of fluid that will satisfy the operating` conditions now to be described. In the design here shownjthatisfsatisfied by'charging the stationary transmission up to"-al'uouttheV level Vindicated L on Fig. l. Suitable filling and draining openings are shown at 6d and 62'.

v The slotsindicated atr23 in Figs. l and Z allow iiuid tok drainV down and contact the journalswh'en the housing cornesv to rest,` to provide additional lubrication for the journals; silicon fluid being a good lubricant.

In operation, duid in the reservoirs 46 and in passages 50 rotates essentially -with the housing, being but little iniuenced in rotational fspeed by the disk. Fluid in the spaces between the 'disk faces 44 and housing faces 42 rotates at a4 speed approximatelymidw'ay between the rotational speeds of the disk and housing.

` Assume first that the disk is the driving member rotating at :constant speed .and that the driven housing is standing still; a theoretic condition at the'start of driving the housing from the disk and the conditionof maximum slip between disk and housing. Under this condition duid is thrown outwardly by the rotating fdisk to fill the annular spaces All, lying outside the radius' R. With those spaces illed, any additional iiuid thrown outwardly by the rotating disk is returned to 'the reservoirs through they stationary passages 50. The spaces A1 under this condition contain iluid fromthe outer periphery at 40 inwardly approximately to the radius R, or to the radial level denoted Maximum Slip in Fig. la. The remainder of the fluid is in passages 5 0 andthe reservoirs, standing essentially still rotationally'and subjected Y'to essentially no Vcentrifugal `force tending to throw it out. At the start of driving the housing the torque is that transmitted by uid shearin the outer 4annular spaces A1 only. j

As the rotational` speed of the housing increases, the

increasing centrifugal 'force on "the fluidin lpassages 59 increases, and forces'iluidl from the outer end of lthose passages into the active space A to progressively decrease the innerradius ofthe fluid in that space. ,The iiuid in that space, as stated before, rotates at a speed intermediate the speed of the disk and that of the housing and is subjected to a corresponding centrifugal force. At any intermediatehousing speed the inner radius of fluid in active spaces A'is that at which the centrifugal force on the fluid inY those spaces balances the centrifugalV force on the fluid in the more slowly rotating passages 5d. Thus, as the rotating speed of the body and the fluid in those passages increases, the inner radius of the fluid in active spaces A decreases.` 'That continuesy until, when the housing reaches the full disk speed,"the inner radii of uid in' the housing passages and in theY active spaces are equal, with centrifugal forcesv in balance onrthose two bodies of fluid. That takes place regardless of the total amount of fluid in the transmission. lf the fluid volume is just enough to fill the active vspaces and passages 50 outwardly Yfrom the outer boundary'ii of the reservoirs, the balance 'at full housing speed places theinner radius of both iluid'bodies at thatboundary-at the line designated no slip in Fig. la. If the total fluid volume exceeds that, theV excess simplyrevolves against the outer y wall 48 of the reservoir in communication with both the -actlve spacesA and passages 50, and therefore does not disturb the balance.

At maximum rotational housing speed-no slip between -the driving disk and the housing-all the fluid is rotating at the full driver speed. The inner level of the iluid in the whole of the spaces A and in the passages 5@ then stands preferably at about the outer delimiting circumference 48 of the reservoirs; at about the radial level indicated No Slip in Fig.V la.' 'Under this condition all of the A fluid V,is preferably'out ofthe reservoirs. Any excess' fhuid' aantasting@ resina' in the outer pans of the reservoirswand be inactive.

At NoSlipthetransmitted 4torque is Zero, because thefluid'inthe active spacesv between the faces of the disk and housing is not in shear between those two parts that then have norelatiye mqvmeut- `:At maximum Slip the transmitted torque is ,basically controlled by the radial width of outer ative 4spaces Alb-by the relative radial width of faces 42a.

The amount of transmitted torque at Maximum Slip (housing stationary) depends on the "radial width of the spaces outside the outer ends of passages 50. By decreasing the radius' of those outer endsk that torque is increased. If that'V radius *is- Vincreased'to -the point where thfe outerv endsof 50 arefat the Vouter periphery of the disk and housing surfaces ted and 442, the torque transmitted at Maximuni Slip approaches zero.

Ihe curve in Fig. 1b shows the torque transmitted through the range ofl slip whenthe disk is the driving member. Y Usedin this manner, the transmission is a torque limiting drive.

If'gon vthe other hand, vthe, housing Y is the driving member, rotatingt"constantf'speed, the uid is, at all times, locatedinthe active spaces A and passages Sti outwardfof the delimiting line 48. The torque transmission, in terms of slip,`is then shown bythe curve in Fig. 1c. Used in .this manner, the transmission is a maximum torque drive. A

Due to the factY that duid actions on opposite faces of both the disland thehousing are the same, iiuid pressures on ythose opposite faces are balanced and no differential pressures tend to bend or distort either the disk or the Vhousingfand-change the active clearances. lfslight diierences in-p'ressures arise from slight inaccuracies of duplication ofthe two halves of the housing, andwhich may occur on-rapidY changes of transmitted torque, the peripheral passage at 40 aroundthe diskl edge tends to equaiize pressure differences'. (The passage at ddmay have the saineV .clearance as the-active spaces A, and thus add its area to the Maximum Slip annular spaces A1. Or, its 'clearance'vmaybe more, tohave more Vequalizing effect.) Ahdafsrie'sof' openings through the disk, as shown at 7 ti, located at about the radiusfof the outer reservoir delimitation 48, is very effective inequalizing incidental ditte-rential pressures. Ihis balance of pressures keeps the disk equally spaced from the housing faces, and eliminates the necessity of high'accuracy in machining and assembly that* would vbe requiredY if Athe' disk Vwere axiallyy fixed on its hub and the hub held against axial movement.

From what has been said' it will be" apparent that the passages 50 need not be in the, form of slots open to activespacesA'throughout their lengths.- V*They need only be in communication with the reservoirsat theirY inner ends and-withactive spaces Ar at their outer ends. It is the centrifugal force on the uid at the outer ends of the slots that forcesuid fromthem into spaces A. Fig. 3 illustrates the indicated modiication, where the passages 50a haveli'nner-Yand outer Hcommunications only at their ends.V Theother Vpartsare ,the same asin Fig. i and are given the fs'anne numerals. A

Eig. 4-show`s ianothermodificationin which the active driving st lrfacearea isfrniltiplied, in comparison to Fig.

l, `utiliiing` multiple disks on the shaft, here shown as peripherally mounted in housing 12 by being clamped between the housing halves. Each housing half is the same as described `for Fig. l, with reservoir 46, slots 50 and active surface 42 including the unbroken annular face 42a outside the outer ends of the slots. The outer faces of disks 16a are spaced from the active housing faces as in Fig. 1, and the inner faces of the disks 16a are similarly spaced from the opposite opposed faces of disk 12a. The peripheral edges of the disks 16a are spaced from the outer shoulder boundary 40 of the housing cavities as in Fig. l; and both disks may also have the openings 70 to facilitate equalization of pressures in spaces A and B. The peripheral spaces at 40, and openings 70, provide for free fluid passage between the active spaces A at the outer faces of the disks 16a and the active spaces B betwen disk 12a and disks 16a.

The functional performance is in substance the same as in Fig. 1. Fluid in the active spaces B rotates at the same angular velocity as in the active spaces A, while fluid in the reservoirs and slots 50 rotates essentially at the speed of the driven member. Spaces A and B being in intercommunication, the radial level of uid in B is at all times the same as that in A. The action is thus in substance the same as in Fig. l; and the lluid actions on opposite faces of each of the three disks being the same, pressure balances are maintained on them as well as on the housing.

I claim:

1. A fluid shear transmissionv comprising in combination driving and driven members relatively rotatable about a common axis, one of said members being in the form of a rigid housing enclosing the other, the enclosed member having opposite faces radially continuous from a predetermined radius outwardly to its periphery, and the housing having rigid and at least partially radially continuous faces spacedly opposing the faces of the enclosed member from said predetermined radius outwardly to the periphery of the enclosed member, said spacings forming active spaces for a fluid in shear, one of said members having fluid reservoir spaces at each of its faces, the inner boundaries of said reservoir spaces being near the rotational axis and the outer boundaries substantially coinciding with said predetermined radius, so that said reservoir spaces directly communicate with said active spaces at said predetermined radius, and one of said members having liuid passages, in addition to the spaces between said faces, in communication with and extending radially outwardly from the reservoir spaces and communicating at their outer ends with the active spaces between the driving and driven members.

2. The combination defined -in claim 1 and in which 6 the said housing faces are inner faces of the housingl Walls.

3. The combination defined in claim 2 and in which the enclosed member is in the form of a single disk.

4. The combination defined in claim l and in which the enclosed member is in the form of a single disk.

5. The combination defined in claim l and in which said passages are in the form of grooves.

6. The combination dened in claim 5 and in which the points of communication at the outer end of said passages are located radially inwardly of the outer peripheral boundary of said active spaces.

7. The combination defined in claim 1 and .in which the points of communication at the outer end of said passages are located radially inwardly of the outer peripheral boundary of said active spaces.

8. The combination of claim 1 and in which the enclosed member is in the form of a single disk with flat opposite faces, the housing faces are flat inner faces of the housing walls directly spacedly opposing the opposite faces of the disk, the reservoir spaces are formed in the i housing, and in which said passages are in the form of grooves sunk into the housing faces and have their points of communication at their outer ends located radially inwardly of the outer peripheral boundary of said active spaces.

9. The combination defined in claim l in which the enclosed member comprises an assemblage of a plurality of spaced-apart disks with opposite faces of the assemblage spacedly opposing the said housing faces to form active spaces for a uid in shear, and including also disk means between the spaced-apart disks and presenting opposite faces to the adjacent faces of said spaced-apart disks to form further active spaces for a liuid in shear.

l0. The combination defined in claim 9, in which the housing faces are inner faces of the housing walls, the reservoir spaces are formed in the housing, and in which said passages are in the form of grooves sunk into the housing faces and have their points of communication at their outer ends located radially inwardly of the outer peripheral boundary of said active spaces.

References Cited in the lile of this patent UNITED STATES PATENTS 2,629,472 Sterner Feb. 24, 1953 2,706,547 Ranzi Apr. 15, 1955 2,743,792 Ransom May l, 1956 FOREIGN PATENTS 53,057 France Sept. 18, 1944 

